Alternative names: Myelodysplastic Syndrome, MDS, Pre-leukemia, Preleukemia, Smoldering Leukemia
Preleukemia, or myelodysplastic syndrome (MDS), is a condition that can occur when some of the blood-forming cells in the bone marrow are damaged, leading to lower numbers of one or more type of blood cells.
The bone marrow is spongy tissue inside some bones, such as the hip and thigh bones. It contains immature cells, called stem cells, which can develop into the red blood cells that carry oxygen through the body, as well as the white blood cells that fight infection, and the platelets that help with blood clotting. When a person has a myelodysplastic syndrome, the stem cells do not mature into healthy blood cells; many die in the bone marrow, leaving a deficit of healthy cells, which can lead to infection, anemia, or easy bleeding.
Because the majority (about two-thirds) of MDS patients do not develop leukemia, MDS was previously classified as a disease of low malignant potential. Now that doctors have learned more about MDS, it is considered to be a form of cancer.
The median age at diagnosis of a MDS is between 60 and 75 years; a few patients are younger than 50; MDS diagnoses are rare in children but a few pediatric cases have been reported. Males are slightly more commonly affected than females. Workers in some industries with heavy exposure to hydrocarbons such as the petroleum industry have a slightly higher risk of contracting the disease than the general population.
MDS occurs when the normally well-controlled production of blood cells is disrupted, resulting in blood cells that are immature and defective. Instead of developing normally, they die in the bone marrow or just after entering the bloodstream. Over time, the number of immature, defective cells begins to surpass that of healthy blood cells, leading to problems such as anemia, infections and excess bleeding.
Risk factors for MDS include:
Anemia dominates the early course of the disease. Most patients who have symptoms complain of the gradual onset of fatigue and weakness, dyspnea, and pallor. However, at least half the patients show no symptoms and their MDS is discovered only during routine blood tests.
Symptoms of MDS are nonspecific but include:
A blood count can show the following signs:
The World Health Organization classifies myelodysplastic syndromes under subtypes based on the type of blood cells involved: red cells, white cells or platelets. The subtypes include:
Fever and weight loss should point to a myeloproliferative rather than myelodysplastic process.
There is no cure for myelodysplastic syndromes. The goals of therapy are to control symptoms, improve quality of life, improve overall survival, and decrease progression to acute myelogenous leukemia (AML).
The outlook for MDS is poor; most patients will progress to acute myeloid leukemia within a few months. The survival rate varies from years to months; stem cell transplantation offers cure, with survival rates of 50% at 3 years, although older patients do poorly.
Possible complications include: